1. Field of the Invention
The present invention relates to an apparatus for severing a paper web, which is being wound onto a rotating drum, for the purpose of initiating the winding of the paper web onto an empty rotating drum. The paper web is severed with a tear strip, which extends transversely in relation to the paper web and whose free end can be fastened to the empty drum. When the free end of the tear strip is fastened to the empty drum, it is helically wound on the drum and it thereby severs the paper web. The apparatus has a carriage which can be displaced along the axis of the empty drum, laterally outside the latter and transversely in relation to this axis, and on which there is disposed a device for holding the tear strip.
2. Description of the Related Art
An apparatus of that type is described in U.S. Pat. No. 4,757,950 to Rodriquez. There, the tear strip (the cutting tape) is pushed through a guide rail extending transversely relative to the paper web, from one side of the paper web to the other side of the paper web, the free end of the tape being located in the region of the nip formed between the two drums. As soon as the severing operation is to be started, the tear strip is advanced by means of a conveying device, so that its free end comes to rest on the empty drum and it is glued to the latter by applying adhesive. As a result, the tear strip is torn out of the guide rail and, due to the rotation of the empty drum, is wound helically on the latter, thereby severing the paper web in the process. The paper web is then wound onto the empty drum.
The conveying device for the tear strip is located on a first side of the paper web and the severing operation is started on the other side of the paper web. It is thus necessary to push the tear strip through the guideway that extends transversely to the paper web, and to push it into the nip between the two drums. The tear strip has to have an adequate stiffness For this purpose, so that it can be pushed to the second side. For this reason, tear strips used for the prior art apparatus are produced from mutually adjacent, adhesively bonded paper cords.
Furthermore, our earlier U.S. Pat. No. 5,725,177 (corresp. to European EP 708 049 A1) discloses an apparatus in which the conveying device for the tear strip is located on that side of the paper web on which the severing operation starts. Since the tear strip is thus pulled through the guideway and only needs to be conveyed toward the empty drum, the tear strip tape may have a significantly lower stiffness. Accordingly, it is possible to use tear strips in that apparatus which are produced, for example, from folded paper sheets, the strips having a significantly lower thickness.
The disclosures of both above-noted disclosures are herewith incorporated by reference.
The tear strips must satisfy two basically contrary objectives. First, the tear strips must have a high tearing strength. Second, they should be as thin as possible, since they are wound onto the empty drum over which the paper web is subsequently wound up, whereby those layers of the paper web which are marked by impressions caused with the tear strip constitute waste. Since the tear strip should be fed to recycling together with the waste paper from the paper web, the tape should or must be produced from paper. In addition, the drums are formed with a rubber coating jacket, so that the tear strip must also be as soft as possible and have the lowest possible stiffness. If all these requirements are satisfied, however, this causes difficulties in conveying the tear strip toward the empty drum so that it comes to rest on the latter and initiates the severing operation.
The apparatus disclosed in the above-mentioned U.S. Pat. No. 4,757,950 is also constructed, on the other side of the paper web, to have a device which is intended to hold the tear strip firmly and which can be guided up to the surface of the empty drum by means of a carriage. As soon as the free end of the tear strip has been fastened to the empty drum, it must be released by the device by which it is being firmly held.
In that prior art apparatus the device that holds the tear strip is formed with two mutually pivoting clamping jaws. Upon starting the severing operation, the tear strip is torn out of these two clamping jaws. Since that tear strip is a stiff tape, it withstands the stress caused by the operation. However, as soon as a significantly thinner tear strip is used, there is a risk of its being destroyed as it is being torn out of the clamping jaws. In that event, it is no longer possible to carry out the severing operation of the paper web.